An ignition coil for an internal combustion engine is mainly made up of a transformer part and a control circuit part and a connecting part, and the transformer part is made up of a iron core which forms an open magnetic path, magnets, a secondary spool, a secondary coil, a primary spool and a primary coil. The grating interference type optical encoder further includes: a phase grating that divides the rediffraction light fluxes superimposed between the diffraction grating and the light receiving element into a plurality of light fluxes, and a linear deflection element having different deflection directions corresponding to the plurality of light fluxes divided by the phase grating. Next, the fist capping layer is removed. The monitoring system may also be external to the region receiving the control commands. The alert mode may include a silent alert mode on the wireless device. As seen in the flow direction of the liquid to be filtered, the connecting channel has a first area, which is arranged directly upstream from the filters and forms a single common liquid distribution space for the two filters.